Speckled dace (Rhinichthys osculus) COSEWIC assessment and status report: chapter 6

Biology

There is very little information on the basic biology of speckled dace. The only published sources of information on the biology of speckled dace in Canadaare Peden and Hughes (1981, 1984) and Peden (1994). McPhail (undated) produced a summary on speckled dace that is available on the UBC website (available in PDF format, 284KB).

Life cycle and reproduction

Laboratory studies (Kaya 1991) have shown that both increasing photoperiod and increasing water temperature induce spawning in speckled dace. Individuals kept at 15ºC in a photoperiod of 14 h light and 10 h dark after June spawned within 1 to 2 days once the water temperature was increased to 18 or 24ºC. Speckled dace kept in aquaria spawned from April to July when maintained at 21 to 29ºC under a natural photoperiod, indicating that spawning can be protracted. Newly fertilized eggs are about 1.8 mm in diameter, adhesive and denser than water; in aquaria eggs were deposited at the base of available stones, on filters and in corners.

No spawning behaviour or spawning sites have been documented in BC. Peden and Hughes (1981) examined ovarian maturity in female speckled dace and suggested that spawning probably starts in mid-July. Data collected on fish in spawning condition during sampling are consistent with this timeline (PDI 2005). Peden and Hughes (1981) also reported that females considered to be in spawning condition contained relatively few large eggs (usually <500) around 1.5 mm in diameter. The number of large eggs in fall-caught females ranged from about 450 to 2,000 suggesting a single ovarian cycle per year. Egg development is rapid following fertilization as hatching occurs in 4-5 days at 24ºC and 6-7 days at 18ºC; newly hatched larvae are about 6 mm long and become free swimming about a week later (depending on temperature); at about 8 mm they emerge from the substrate and begin to actively feed (McPhail 2003).

Newly emerged fry appear in the river in early August at a size of around 9 mm; by late October they are about 20-30 mm in fork length (McPhail 2003). Length frequency histograms from sampling in July and August of 2000 and 2001 suggest the presence of at least three size classes or age groups (PDI 2005). Most males in the Kettle River mature at the end of their second summer (at age 1+) and spawn for the first time the next summer (age 2+). Females typically become sexually mature one year later than the males. Speckled dace do not mature until they are around 40 to 50 mm in length (Peden and Hughes 1984). While there are no detailed data on age structure, field sampling indicates that the adult population is comprised mostly of fish <60 mm in fork length (those in their second or third summer); females, which occasionally reach fork lengths over 90 mm are likely in their fourth summer (age 3+) (Peden and Hughes 1981, 1984; Peden 1994; McPhail 2003).

Peden and Hughes (1984) observed an abundance of young fish in the Kettle River and suggested that reproductive potential was high. Although they caught fewer males than females, they were unable to effectively sample faster water sites where larger males might be found. Males are rare in most collections, suggesting possible sex-related differences in microhabitat utilization (Peden and Hughes 1984; McPhail 2003).

Herbivory/Predation

The stomach contents of adult speckled dace show that they consume the larvae of aquatic insects and significant amounts of filamentous green algae; some specimens collected in September contained winged insects (Peden and Hughes 1981; Peden 1994, 2002; McPhail 2003). Peden (2002) noted that the intestine of speckled dace is not long and coiled as typically found in herbivores and suggested that algae had been ingested inadvertently. The small number of juveniles that have been examined suggest a diet similar to the adult fish; however, they did contain a larger proportion of algae, diatoms and chironomids (McPhail 2003).

Physiology

No studies have been documented on the physiology of speckled dace.

Dispersal/Migration

There are no reports of speckled dace migrations in the literature, although Minckley (1973) did refer to the ability of speckled dace to re-colonize isolated refuges in Arizona rivers following devastating floods. Young-of-the-year speckled dace do disperse from shallow, low velocity habitat to deeper, faster water as they grow (Peden and Hughes 1981, 1984). Speckled dace in Canada are reproductively isolated from other populations downstream of Cascade Falls (a 30.5 m natural barrier preventing upstream migration). Movement across the US border between the Canadian and American sections of the Kettle River above Cascade Falls is possible. Any speckled dace that move or are flushed over the falls are unable to return to the population upstream.

Interspecific interactions

Speckled dace co-occur with chiselmouth (Acrocheilusalutaceus), pikeminnow (Ptychocheilus oregonensis), redside shiner (Richardsonius balteatus), longnose sucker (Catostomus catostomus), bridgelip sucker (Catostomus columbianus), largescale sucker (Catostomus macrocheilus), rainbow trout (Oncorhynchus mykiss), introduced brook trout (Salvelinus fontinalis), mountain whitefish (Prosopium williamsoni), mottled sculpin (Cottus bairdii), and slimy sculpin (Cottus cognatus) in the Kettle River system above the falls. Speckled and Umatilla dace coexist for a short section below Cascade Falls, but Umatilla dace appear to replace speckled dace about 10 km below the US border likely through competitive exclusion (Peden and Hughes 1988).

Species interactions have not been studied in the Kettle River system. Baltz et al. (1982) found that competitive interactions between speckled dace and riffle sculpin (Cottus gulosus) for preferred microhabitat in a California stream were influenced by water temperature.

Adaptability

Adaptability to changes in habitat has not been investigated in speckled dace in Canada. Generalizations from case studies in the US may be misleading due to the extent of adaptive diversity observed among populations in different drainages (Peden 2002, McPhail 2003). Since speckled dace are warm-water adapted they may be able to benefit from the warmer temperatures associated with climate warming; whether they can also adapt to the associated decrease in summer flows and the consequential degradation of habitat and reduction in food supply from riffles is unknown. Peden (2002) speculated that the current presence of large speckled dace in the area above the old dam near Cascade Falls may demonstrate the ability of the species to respond to habitat improvement or the restoration of natural flows following weir/dam removal. 

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